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The most common energy storage is the electrical battery combined with electric generator-motor parallel or in series with the combustion engine. This solution is already represented on the market by Toyota Prius and Honda Insight among others.
This concept seem to become very popular through the new ISG solutions providing "mild hybrid" characteristics. The drawbacks of this technology are mainly added cost and weight, maintenance and electric fields. Lately, some "hydraulic Hybrids" have appeared on the market. The Ford/Eaton HLA, Hydraulic Launch Assist using hydraulic pumps to brake or accelerate the vehicle. The drawbacks here are the added cost and maintenance of the hydraulic system. In the Hedman combustion cycle it is natural to use compressed air as energy storage, alternating the compressor strokes with power strokes. This way, we obtain the "hybrid" functions of energy recovery (braking) and low load elimination at no extra cost. This would also work with other combustion cycles like Otto or Diesel. We believe pressurized air has many advantages for energy storage: Little extra hardware Low weight Environmentally friendly Harmless even if leaking Robust function High efficiency New opportunities for increased and instant engine torque |
Cargine is running a project to investigate this concept at Lund University since Jan 2006. Results have been published in SAE paper 2007-01-0288. Further results will soon be published, including a measured regenerative efficiency of 40-48 %
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The Pneumatic Hybrid
A hybrid solution generally contain a combustion engine, an energy accumulator and a device to store and retrieve energy from this accumulator.
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